President Trump and Vietnamese President Tran Dai Quang attend a ceremony at the presidential palace in Hanoi in November 2017. (Hoang Dinh Nam/AFP/Getty Images)

DOES AMERICA really have the capability to influence other nations toward the ideals of democracy, free markets, rule of law and respect for human rights? Often it seems not when dictators, strongmen and party bosses engage in abominable behavior, silencing critics and imprisoning civil society activists. But the case of Vietnam and the Trans-Pacific Partnership suggests that other nations, including the most authoritarian, do pay attention to U.S. prompts.

As Simon Denyer and David Nakamura reported in The Post this month, the Trans-Pacific Partnership (TPP), a 12-nation trade agreement that was the centerpiece of President Barack Obama’s approach to Asia, was in trouble by late 2016. It was not yet approved by Congress, it faced serious opposition at home, and Democratic presidential nominee Hillary Clinton had signaled her intention to pull out of an agreement she once called the “gold standard” of trade deals.

But the pact had power in Vietnam, one of the signatories. The agreement secured promises from Vietnam’s Communist Party rulers to make space for independent trade unions, outlaw child labor, give private firms more opportunity to compete with the state sector, strengthen environmental controls and allow an unfettered Internet. In exchange, the Vietnamese would gain greater access to the huge U.S. market. Also, one of Vietnam’s regional rivals, China, was excluded. And TPP came at a time when a budding movement of brave Vietnamese activists was using social media to spread ideas about workers rights, transparency, accountability and democracy.

Then, in his first week in office, President Trump withdrew from TPP on the dubious complaint that it was bad for U.S. businesses and workers. The impact in Vietnam was unmistakable. As former U.S. ambassador to Vietnam Ted Osius told The Post, “It pulled the rug out from under the reformers.”

No longer bound by the TPP restrictions, Vietnam’s rulers set out to punish the activists. The regime detained a blogger known as Mother Mushroom, whose real name is Nguyen Ngoc Nhu Quynh and who wrote extensively about a big chemical spill in 2016 that devastated marine life and galvanized protests against the regime. In June 2017, she was sentenced to 10 years in prison for “conducting propaganda against the socialist state.” (Last Wednesday she was released from prison and left for the United States.) The authorities also attempted to crush Brotherhood for Democracy, a group founded by lawyer Nguyen Van Dai. On April 5, 2017, a court in Hanoi sentenced him and five other activists to between seven and 15 years in prison for alleged subversion. Mr. Dai has since been sent into exile in Germany, while others remain behind bars. He told The Post that if the United States had remained in TPP, “it would have been a chance to change my country.”

Change does not come easy. China never fulfilled the hopes of those in the West who thought freer trade would temper the authoritarian leadership. But abandoning the cause of democracy and human rights almost always will enable more repression, while championing these values can get results, however uneven and imperfect.